1. Field of the Invention
The present invention relates to a sound system with a howling-prevention function.
2. Description of the Related Art
As shown in FIG. 1, a sound system such as a public address system, is designed to receive voice or the like at a microphone 1 for thereby converting the same into a microphone signal, and thereafter to amplify the microphone signal as an output audio signal of the microphone 1 with a microphone amplifier 2 and a power amplifier 3 thereby to produce sound from a speaker 4. Such a sound system often develops howling when one attempts to turn up the volume or to bring the microphone 1 close to the speaker. The howling is produced by forming repeatedly carried out positive feedback loop in which sound corresponding to the microphone signal is produced from the speaker 4 and the produced sound is received at the microphone 1 again thereby to be reproduced from the speaker 4.
In order to avoid such howling, there is provided a sound system including the microphone amplifier 2 having frequency characteristics in which high frequency components have been cut off. In addition, as shown in FIG. 2, there is also provided a sound system of such a type that an A/D converter 5, a delay circuit 6 and a D/A converter 7 are disposed between the microphone amplifier 2 and the power amplifier 3 thereby causing a delay time interval introduced by the delay circuit 6 to vary with the elapse of time in response to an output signal from an oscillator 8, thereby to subject the same to digital processing.
However, the former is accompanied by the problem that there is no effect on the howling caused by signal components other than the high frequency components as well as deterioration in the sound quality because high frequency components of the microphone signal are omitted or disregarded. In addition, the latter is also accompanied by the problem that since the microphone signals within all bands are delayed, a chorus phenomenon appears in the sound issued at the speaker, thereby causing inferior sound quality.